1. Field of the Invention
The system of this invention resides in the area of semi-trailer landing gear extension and retraction mechanisms and more particularly relates to an electrically activated pneumatic system for the raising and lowering of a semi-trailer's landing gear for positioning and/or raising and lowering the trailer.
2. Description of the Prior Art
Many semi-trailers have front landing gear for support of the front of the trailer when the tractor is detached. Such landing gears generally have two spaced-apart, jack-type structures joined by a cross-driven shaft engaged into a gear reduction box assembly. The gear reduction box assembly is driven by a manually operated crank. The gear reduction box assembly can have two gearing ratios: a low gear and a high gear. The gear ratio utilized within the gear reduction box assembly depends upon the lateral positioning of the crank shaft. Manually operated jack structures are often difficult to use, require much time for their operation and expose the operator to potential injuries as he is positioned next to the trailer while turning the crank to raise or lower the landing gear to in turn raise or lower the trailer.
The prior art includes many devices for the motorized extension and retraction of landing gear apparatuses for semi-trailers. Many of these prior art systems require their installation on the semi-trailer at the time of its construction or at the time of the installation of the landing gear thereon. Typical of such prior art in U.S. Pat. No. 4,466,637 to Nelson which discloses an electric motor to drive the usually manually operated crank system for raising and lowering of the semi-trailer landing gear. The prior art also teaches that when using electric motors, such motors can be controlled from within the cab of the vehicle such as taught in U.S. Pat. No. 4,097,840 to Chappelle. Pneumatically powered actuators for raising and lowering the semi-trailer's landing gear are disclosed in U.S. Pat. Nos. 4,400,986 and 4,402,526 both owned by the Atwood Vacuum Machine Company. These patents disclose a complex structure to receive pressurized air for the actuators to rotate the crank shaft of the gear reduction assembly to raise and lower the landing gear. U.S. Pat. No. 4,345,779 to Busby discloses a pneumatically operated drive unit attached to the shaft of the gear reduction box assembly which drive unit is disposed to the outboard side of the gear box and utilizes a pneumatic impact motor which is attached to a nut member welded to the end of the gear reduction box assembly drive shaft. These types of units, though, provide a pulsating drive that is not conductive to the desired smooth operation of raising and lowering the landing gear legs. U.S. Pat. No. 3,874,696 to Gardner teaches that a landing gear can be pivoted rearward or forward by an air cylinder receiving air from the air brake line or the emergency air brake line of the trailer. The landing gear of Gardner is not directly adjustable up and down by a gear system and cannot raise or lower the trailer. Other means for the raising and lowering of landing gear are known in the prior art such as the use of hydraulic pistons as disclosed in U.S. Pat. No. 3,503,588 to Bach. The hydraulic system of Bach is large and cumbersome, and hydraulic pistons do not provide the same positive holding as provided by a gearing arrangement. Power failure or loss of pressure could cause failure and collapse of the landing gear.
Because of the complexity and expense of prior art systems for raising and lowering semi-trailer landing gear, they have not been widely accepted in the trucking industry. Also because of the prior art's complexity and need for specialized parts, many of which have proven to be fragile, they have been generally unsuitable to the rugged demands of over-the-road semi-trailers in use of a daily basis.